Without purification both the gaseous and liquid products from a slurry bubble column Fischer-Tropsch reactor will contain catalyst particles.
The gas phase at the top of a slurry bubble column reactor will contain small amounts of entrained liquid and catalyst particles. The largest catalyst particles will to some extent fall down to the slurry phase again by gravity, but the remaining catalyst particles will leave the reactor with the gaseous product, unless they are separated from the gas phase. As a result of the particle size separation, the catalyst particles which remain in the gas phase will be smaller than the average particle size in the slurry phase. Entrained catalyst particles which not are separated from the gas will cause unwanted loss of catalyst, as well as problems downstream of the reactor such as agglomeration of catalyst particles at specific locations, with the possible formation of hot spots, fouling of heat exchangers due to deposition of liquid and catalyst particles, and contamination of the condensed liquid product with catalyst particles.
The slurry phase in a slurry bubble column reactor contains catalyst particles and produced liquid. The produced liquid is separated from the slurry for instance in cylindrical porous metal filter elements. The liquid product after such a filtration, denoted as primary liquid filtrate, will contain at least minor amounts of catalyst particles. These catalyst particles will typically have a particle size smaller than or equal to the pore openings in the filters inside the slurry bubble column reactor. If these particles not are separated from the liquid product, they will cause unwanted loss of catalyst, as well as problems downstream of the reactor, such as agglomeration of catalyst particles at specific locations, with possible fouling of heat exchangers due to deposition of liquid product with catalyst particles. The liquid product from an F-T synthesis is usually further refined, in hydrocracking/hydroisomerisation units, and the catalyst in such units will tolerate only very low levels of F-T catalyst particle contamination. In some such applications, the particle concentration in the liquid product must be as low as 10 ppmw.
EP 592176 A discloses a slurry bubble column reactor including a number of filter cartridges in the upper part of the reactor. Liquid hydrocarbon product is removed from the region above the filter cartridges.